1. Field of the Invention
This invention relates to an improved shear ram cutting blade configuration for use in a shearing ram for a ram-type blowout preventer used in oil and gas drilling and workover operations. Ram-type blowout preventers are part of a pressure control system used in oil and gas drilling operations to control unexpected well bore pressure spikes or "kicks" as they are commonly referred to in the industry.
The blowout preventer has a body with a vertical bore and a pair of laterally disposed opposing bonnet assemblies. Each bonnet assembly includes a piston which is laterally moveable within the bonnet assembly by pressurized hydraulic fluid. The opposite end of the pistons each have a connecting rod attached thereto which in turn has a shear ram mounted thereon. These shear rams are designed to shear or cut through any member, such as tubing or seismic logging cable, disposed within the blowout preventer body's vertical bore. This sudden closing of the rams is necessary when a well bore pressure spike or kick is detected during downhole operations such as well logging or well maintenance. Due to the need to rapidly seal the well bore, there is insufficient time to retrieve the aforementioned tubing or cable from the well bore before closing the rams. Therefore it is necessary to have shear rams that can cleanly cut through these members and seal the well bore.
These shear rams face a difficult task. Recent requirements promulgated by some drilling contractors include the ability of the shear rams to shear up to ten strands of cable, multiple strings of steel tubing or a combination of the two, or multiple strings of a composite tubing with electrically conducting wires in the wall. Each of these requirements poses similar yet different requirements on the shear rams. In the case of multiple strands of cable the flexibility of the cable along with its inherent toughness makes it particularly difficult to shear or cut cleanly without leaving partially cut strands of the cable in the blowout preventer bore and thereby making it especially difficult for the shear rams to seal after the cutting or shearing operation. Shearing multiple strings of tubing poses an almost opposite problem in that their rigid structure causes the individual strings of tubing to flatten and extend beyond the outer edges of the shear ram cutter blades as they are initially squeezed by the blades. This can cause unsheared pieces of tubing to interfere with the closing operation of the shear rams and difficulties in sealing.
Thus, the shear rams in a ram-type blowout preventer must be able to cleanly shear a variety of members and seal the blowout preventer bore afterward in daily operation. The double shearing rams of the current invention offer a significant improvement over existing shear ram designs without requiring any changes to the existing blowout preventer design.
2. Description of Related Art
U.S. Pat. No. 5,501,424 to M. R. Williams et al. gate valve adapted for cutting wireline using an insert in the gate and seat for shearing a wireline cable disposed therein.
The shearing gate valve apparatus shown in U.S. Pat. No. 5,803,431 to L. G. Hoang et al. discloses a gate with a layer of hard facing material welded to the face of the gate to ensure the gate does not form an upset during shearing operations that would interfere with sealing operations.